1. Field of the Invention
The present invention relates to a vinyl chloride fiber for use in artificial hair such as wigs, hairpieces, braid, extension-hair and accessory hair, or for use in fibers for dolls' hair such as doll-hair, and a process of producing the same.
2. Description of the Related Art
Vinyl chloride fibers produced by spinning vinyl chloride resins into fibers, on account of its superiority in strength, elongation, curl-keeping property and styling property, are much used in fibers for artificial hair for the decoration of hair or fibers for doll's hair such as doll-hair.
Hitherto, as fibers for artificial hair for the decoration of hair, in order to industrially produce fibers having a small degree of fineness (small cross-section and fine fibers), the wet spinning method that generally employs solvents for producing vinyl chloride resins or the dry spinning method is used. The wet-spinning method, however, has disadvantages that since solvents are used in the method with a result that a desolvating process is required, an excessive investment for installation is required, and the maintenance thereof needs many hands. In addition, in order to improve the solubility of the resins with solvent, copolymerization with a co-monomer such as acrylonitrile is carried out. As a result, there are problems that it is colored at an initial stage, it is liable to change to strong yellowish hair due to heat in a drying process, or it is not sufficient in the curl-keeping property for the fibers.
On the other hand, the melt spinning method is known as a spinning process in which no solvent is used. However, in order to obtain by this method fibers having a small fineness for artificial hair for the decoration of hair or the like and having a semi-gloss surface (evaluation standards thereof are shown in examples) and feel which are extremely similar to that of human hair, it is preferred that the resins are caused to melt and run-off through nozzle orifices the sectional areas of which are extremely small (0.5 mm.sup.2 or less), thereby making a spinning draft ratio small (Dr ratio: 25 or less). In other words, adversely, if the resins are melt and run-off through nozzle orifices each having a larger sectional area to produce vinyl chloride fibers having a small fineness, the spinning draft ratio thereof is naturally required to be increased. As a result, undrawn filament results in being excessively drawn upon melt spinning. Therefore, the surface of the fiber (drawn filament) obtained by drawing and heating the undrawn fiber becomes smooth, has a luster, and lacks the dry feel. As a result, the product is prone to become fibers unsuitable for artificial hair fiber such as the hair decoration. Thus, in order to produce a high-quality fiber as the artificial hair fiber such as hair-decoration, melt and run-off is preferably conducted through the nozzle having the cross-section thereof as small as possible, so that the spinning draft ratio may become small.
However, there have conventionally been such problems that when a run-off is conducted through such a nozzle having an extremely small cross-section thereof, the pressure to the nozzles becomes larger than the designed pressure of an extruder, and when an extruding amount is set to be small so as to allow the pressure to be smaller than the rating, the productivity of melt spinning becomes low. Also, there was such a tendency that when the melt spinning temperature is set as high so as to reduce melting viscosity, thermal decomposition occurs and long-run property is decreased.
Accordingly, a wide variety of proposes for this process have so far been described in order to solve these problems, but have not solved completely. For example, Japanese Patent Publication No. Sho 51-2109 proposes to improve spinnability by using both vinyl chloride resin and methyl methacrylate resin. However, a fiber is drawn from a relatively large cross-section to a small section to obtain a fiber having a small fineness. As a result, the surface of the fiber becomes smooth thereby being liable to generate a luster, and resulting in imperfection as an artificial hair fiber because the fiber is not only still far from a semi-gloss surface like human hair, but also have no much dry feel. Additionally, in order to reduce melting viscosity of composition, the process in which Cd--Pb based thermal stabilizers comprising cadmium or lead and lubricants are used, is industrially carried out. However, the use of such formulation ingredients allows to solve difficulties in a nozzle pressure and productivity in melt spinning, while a coloring at an initial stage is intensive, and the product hair is prone to have a strong yellow tint. Further, because such formulation ingredients are very toxic, they are unfavorable either for production process or for a human safety and health due to et direct contact with human head skin as an accessory hair. Still further, this process raises the problem in which when disposed such the hair decorations get mixed in general garbage to cause environmental pollution.